Methods and compositions for the inhibition of Stat5 in prostate cancer cells

ABSTRACT

The present invention relates to compositions and methods for the treatment of prostate cancer. In certain embodiments, the invention relates to compositions and methods for the inhibition of prostate cancer cell growth, comprising inhibiting the activity of Stat5 in prostate cancer cells.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/554,123 filed on Aug. 21, 2006 now abandoned, which is a nationalstage filing under 35 U.S.C. 371 of International ApplicationPCT/US2004/012799, filed on Apr. 23, 2004, which claims the benefit ofpriority of U.S. Provisional Application, 60/465,014, filed on Apr. 23,2003, by Marja Nevalainen, entitled “Inhibition of Transcription FactorStat5 Induces Cell Death of Human Prostate Cancer Cells”. The entireteachings of the referenced Applications are hereby incorporated byreference in their entirety. International Application PCT/US2004/012799was published under PCT Article 21(2) in English.

FUNDING

Work described herein was funded, in whole or in part, by NationalInstitutes of Health Grant Numbers RO1 CA83813 and RO1 DK52013 andDepartment of Defense Grant DAMD 17-01-1-0059. The United Statesgovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

Currently the only pharmacological strategy for the treatment ofprostate cancer is ablation of androgens, either as adjuvant therapyafter surgery or as a primary therapy for patients who are deemed unfitfor surgery. A central clinical problem in prostate cancer treatment isthat residual cancer cells inevitably will overcome androgen ablation,and recur as androgen-independent cancer with increased malignancy.Furthermore, for established androgen-independent and metastaticprostate cancer, the only current treatment options are radiation andchemotherapy, which both are relatively ineffective and associated witha number of negative side-effects. Therefore, better treatmentstrategies for prostate cancer are needed.

SUMMARY OF THE INVENTION

Described herein are compositions and methods for inhibiting cancer cellgrowth by inhibiting the activity of Stat5 in prostate cancer cells. Incertain embodiments, the invention provides a method of inhibitingprostate cancer cell growth, comprising inhibiting Stat5 activity in theprostate cancer cells. Any type of prostate cancer cell, including, forexample, primary prostate cancer cells, advanced prostate cancer cells,and metastatic prostate cancer cells, may be employed in the methods andcompositions of the subject invention.

In certain embodiments, the invention relates to a method of inhibitingprostate cancer cell growth, comprising inhibiting Stat5 activity in theprostate cancer cells by contacting the prostate cancer cells with aninhibitor of Stat5 activity. In certain embodiments, the contacting theprostate cancer cells with an inhibitor of Stat5 activity results inprostate cancer cell death. In certain embodiments, the inhibitor ofStat5 activity is selected from the group consisting of a smallmolecule, an siRNA (short interfering RNA) construct, an antisenseconstruct, and an antibody. In further embodiments, the inhibitor ofStat5 activity is a nucleic acid, which encodes a protein that hasdominant-negative Stat5 function. In certain embodiments, the proteinthat has dominant-negative Stat5 function is selected from the groupconsisting of: mutated Stat5a and mutated Stat5b. Optionally, themutated Stat5a is Stat5aΔ713. Optionally, the mutated Stat5 is atyrosine phosphorylation deficient mutant of Stat5 or a DNA-bindingdeficient mutant of Stat5. In certain embodiments, the inhibitor ofStat5 activity is a nucleic acid, which encodes a protein that hasdominant-negative Jak2 function.

In certain embodiments, the agent that inhibits Stat5 activity is anantisense construct.

In yet other embodiments, the subject invention provides a method ofinhibiting prostate cancer cell growth, comprising inhibiting Stat5activity in the prostate cancer cells by contacting the cells with aninhibitor of Stat5 activity that is an siRNA construct. In certainembodiments, the siRNA construct inhibits the activity of a Stat5polypeptide. In further embodiments, the Stat5 polypeptide is selectedfrom the group consisting of: Stat5a and Stat5b. In additionalembodiments, the siRNA construct inhibits the expression of a Stat5polypeptide, such as a Stat5a or Stat5b polypeptide. In certainembodiments, the siRNA construct comprises Stat5 nucleic acid, such as,for example, Stat5a nucleic acid or Stat5b nucleic acid. In additionalembodiments, the siRNA construct comprises Jak2 nucleic acid andinhibits the expression of a Jak2 polypeptide. In certain embodiments,the siRNA construct comprises Jak2 nucleic acid and inhibits theactivity of a Jak2 polypeptide.

The invention additionally relates to a method of inhibiting prostatecancer cell growth, comprising inhibiting Stat5 activity in the prostatecancer cells by contacting the cells with an inhibitor of one or moreStat5 kinases. Examples of Stat5 kinases that may be inhibited are Jak1,Jak2, Jak3, Tyk2, Src, Fyn, Yes, Lck, Hck, Blk, Fgr, and Lyn. In certainembodiments, the inhibitor is a small molecule.

In additional embodiments, the invention provides a method of inhibitingprostate cancer cell growth, comprising inhibiting Stat5 activity in theprostate cancer cells by contacting the prostate cancer cells with aninhibitor of prolactin. Optionally, the prolactin inhibitor is anantibody to a prolactin receptor.

In certain embodiments, the methods and compositions of the inventionrelate to treating prostate cancer in a male. In certain embodiments,the invention relates to a method of treating prostate cancer in a malein need of such treatment, comprising administering to the male aninhibitor of the activity of Stat5 in prostate cancer cells.

In certain embodiments, the invention provides a method of treatingprostate cancer in an male, comprising administering to the male aninhibitor of the activity of Stat5 in prostate cancer cells, wherein theprostate cancer cells are selected from the group consisting of primaryprostate cancer cells, advanced prostate cancer cells, and metastaticprostate cancer cells. Primary prostate cancer cells are organ confined.Advanced prostate cancer refers to high histological grade, organconfined prostate cancer cells. Metastatic prostate cancer cells are nolonger organ confined.

In additional embodiments of the invention, the invention relates to amethod of treating prostate cancer in a male, comprising administeringto the male an inhibitor of the activity of Stat5 in prostate cancercells, wherein the inhibitor of the activity of Stat5 is selected fromthe group consisting of a small molecule, an siRNA construct, anantisense construct, and an antibody.

The invention also provides a method of diagnosing or aiding in thediagnosis of prostate cancer in a male, comprising obtaining a sample ofprostate tissue from a male and determining whether activated Stat5 ispresent in cells of the prostate tissue sample, wherein the presence ofactivated Stat5 is an indication of prostate cancer in the male. Incertain embodiments, the prostate cancer is primary prostate cancer,advanced prostate cancer or metastatic prostate cancer. In additionalembodiments of the invention, activated Stat5 is detected by means of amethod selected from the group consisting of immunohistochemistry,immunocytochemistry and DNA-binding assays. In certain embodiments ofthe invention, the activated Stat5 detected is nuclear Stat5.

In further embodiments, the invention provides a method of treatingprostate cancer in a male, comprising administering to a male in need oftreatment thereof a therapeutically effective amount of an agent (drug)that inhibits the activity of Stat5 in prostate cancer cells, whereinthe activity of Stat5 is inhibited in prostate cancer cells of the male.In certain embodiments, the prostate cancer is primary prostate cancer,advanced prostate cancer, or metastatic prostate cancer. In additionalembodiments, the inhibitor of the activity of Stat5 is selected from thegroup consisting of a small molecule, an siRNA construct, an antisenseconstruct, and an antibody.

In other embodiments, the invention relates to a method of treatingprostate cancer in a male, comprising administering to a male in need oftreatment thereof a therapeutically effective amount of an agent thatinhibits the activity of Stat5 in prostate cancer cells, wherein theactivity of Stat5 is inhibited in prostate cancer cells of the male. Incertain embodiments, the invention provides an inhibitor of Stat5 thatis a nucleic acid, which encodes a protein that has dominant-negativeStat5 function. In certain embodiments, the protein encoded is selectedfrom the group consisting of mutated Stat5a and mutated Stat5b.Optionally, the mutated Stat5a is Stat5aΔ713. Optionally, the mutatedStat5 is a tyrosine phosphorylation deficient mutant of Stat5 or aDNA-binding deficient mutant of Stat5. In certain embodiments, theinvention provides an inhibitor of Stat5 that is a nucleic acid, whichencodes a protein that has dominant-negative Jak2 function.

In certain embodiments of the invention, an agent that inhibits Stat5activity is an antisense construct.

In additional embodiments, the invention relates to the inhibition ofStat5 activity through the use of siRNA. For example, siRNAs of theinvention are effective in silencing nucleic acid molecules whichinclude Stat5 nucleic acid (e.g., mRNA) as well as the nucleic acid(e.g., mRNA) of activators of Stat5, including Stat5 kinases, such asJanus kinase-2 (Jak2). The siRNA is effective in silencing a nucleicacid molecule (e.g., interfering with or preventing the expression of agene or gene product), which nucleic acid molecule encodes, for example,a Stat5 polypeptide. The terms peptides, proteins and polypeptides areused interchangeably herein. In certain embodiments, an siRNA constructof the invention is effective in inhibiting the activity of a Stat5polypeptide. In further embodiments, the Stat5 polypeptide is selectedfrom the group consisting of Stat5a and Stat5b. In certain embodiments,an siRNA construct of the invention is effective in inhibiting theexpression of a Stat5 polypeptide. In further embodiments, an siRNAconstruct of the invention is effective in inhibiting the expression ofa Stat5 polypeptide selected from the group consisting of Stat5a andStat5b. In further embodiments, the invention relates to an siRNAconstruct that is directed to Stat5 nucleic acid (e.g., mRNA), such asStat5 nucleic acid selected from the group consisting of Stat5a nucleicacid and Stat5b nucleic acid.

In yet other embodiments, the invention provides a method of treatingprostate cancer in a male, comprising administering to a male in need oftreatment thereof a therapeutically effective amount of an agent thatinhibits the activity of Stat5 in prostate cancer cells, wherein theactivity of Stat5 is inhibited in prostate cancer cells of the male andwherein Stat5 activity is reduced through the inhibition of one or moreStat5 kinases. In further embodiments, the invention relates toinhibition of a Stat5 kinase selected from the group consisting of Jak1,Jak2, Jak3, Tyk2, Src, Fyn, Yes, Lck, Hck, Blk, Fgr, and Lyn. In certainembodiments of the invention, an inhibitor of one or more Stat5 kinasesis a small molecule. In other embodiments, an inhibitor of Stat5 is anucleic acid, which encodes a protein that has dominant negative Jak2function.

In further embodiments, the invention provides a method of treatingprostate cancer in a male, comprising administering to a male in need oftreatment thereof a therapeutically effective amount of an agent thatinhibits the activity of Stat5 in prostate cancer cells, wherein theactivity of Stat5 is inhibited in prostate cancer cells of the male andwherein Stat5 activity is reduced through the inhibition of prolactin.In certain embodiments of the invention, Stat5 activity is reducedthrough inhibition of prolactin by an antibody to a prolactin receptor.

In further embodiments, the invention provides a method of treatingprostate cancer in a male, comprising administering to a male in need oftreatment thereof a therapeutically effective amount of an agent thatinhibits the activity of Stat5 in prostate cancer cells, wherein theactivity of Stat5 is inhibited in prostate cancer cells of the male andwherein inhibition of the activity of Stat5 in prostate cancer cells ofthe male results in prostate cancer cell death.

The invention additionally relates to a method for identifying an agentthat inhibits Stat5 activity in prostate cancer cells, comprising (a)contacting a prostate cancer cell or tissue sample comprising prostatecancer cells with a candidate agent and (b) determining the effect ofthe agent in (a) on the activity of Stat5, wherein if there Stat5activity determined in (b) is less than Stat5 activity in an appropriatecontrol sample, an inhibitor of Stat5 activity is identified. A controlsample is an equivalent sample of prostate cancer cells or tissuecomprising prostate cancer cells in which Stat5 is activated, whichcells or tissue samples have not been treated with the candidate agent.A test sample is equivalent to the control sample except that it iscontacted with a candidate agent. For example, the cells or tissuessamples of (a) are test samples. A control may be run simultaneouslywith the test sample, or it may be pre-established.

In further embodiments, the invention provides a diagnostic method forpredicting responsiveness to Stat5 inhibition therapy for treatment ofprostate cancer, comprising (a) obtaining a sample of prostate tissuefrom a male in need of treatment for prostate cancer and (b) determiningwhether activated Stat5 is present in cells of the prostate tissuesample, wherein if activated Stat5 is present, it is predictive ofresponsiveness to Stat5 inhibition therapy for treatment of prostatecancer. In certain embodiments, the prostate cancer is primary prostatecancer, advanced prostate cancer, or metastatic prostate cancer.

In additional embodiments, the invention relates to the use of aninhibitor of Stat5 activity to prepare a medicament to inhibit prostatecancer cell growth. In further embodiments, the invention relates to theuse of an inhibitor of Stat5 activity to prepare a medicament to treatprostate cancer in a male in need of treatment thereof.

The practice of the present invention will employ, unless otherwiseindicated, conventional techniques of cell biology, cell culture,molecular biology, microbiology, recombinant DNA, and immunology, whichare within the skill of the art. Such techniques are explained fully inthe literature. See, for example, Current Protocols in Cell Biology, ed.by Bonifacino, Dasso, Lippincott-Schwartz, Harford, and Yamada, JohnWiley and Sons, Inc., New York, 1999; Gene Targeting: A PracticalApproach, IRL Press at Oxford University Press, Oxford, 1993; GeneTargeting Protocols, Human Press, Totowa, N.J., 2000; Molecular CloningA Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis(Cold Spring Harbor Laboratory Press: 1989); Culture Of Animal Cells (R.I. Freshney, Alan R. Liss, Inc., 1987); Gene Transfer Vectors ForMammalian Cells (J. H. Miller and M. P. Calos eds., 1987, Cold SpringHarbor Laboratory); Methods In Enzymology, Vols. 154 and 155 (Wu et al.eds.), Immunochemical Methods In Cell And Molecular Biology (Mayer andWalker, eds., Academic Press, London, 1987).

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A. Stat5 is activated in human prostate cancer. Detection ofactivated Stat5 in prostate cancer by immunohistochemical analysis usingeither anti-phosphoTyrStat5 antibody (panel a) or a pan-Stat5 antibodyto detect nuclear localized Stat5 (panel b). Anti-phosphoTyrStat5staining was negative in normal, secretory human prostate epithelium(panel c). Positive control staining was obtained from normal humanbreast tissue (panel d) and parallel sections stained withsubtype-specific mouse IgG were negative (e).

FIG. 1B. Stat5 is expressed and activated in human prostate cancer celllines CWR22Rv and LnCap, but not in PC-3. Protein immunoblotting wasperformed as indicated with either anti-phosphoTyrStat5 (anti-Stat5pY),anti-Stat5a, or anti-Stat5b on immunoprecipitated (IP) Stat5a or Stat5bfrom lysed prostate cancer cells that had been harvested duringexponential growth (low-density; LD) or at confluency (high density;HD).

FIG. 1C. Adenoviral delivery of dominant-negative Stat5 (AdDNStat5)induced cell death in androgen-independent CWR22Rv human prostate cancercells. Representative experiment showing a dose-dependent effect on cellviability of adenoviral gene delivery of a dominant-negative Stat5mutant (AdDNStat5) introduced into CWR22Rv cells. AdStat5WT and AdLacZserved as controls. The increasing viral doses used were 0, 1, 2.5, 5,and 10 MOI, and cell viability was measured after 96 h by the MTTmetabolic activity assay. Error bars indicate SD of triplicatedeterminations.

FIG. 1D. Morphology of cell death induced by AdDNStat5 in CWR22Rv andLnCap cells is consistent with apoptosis. Microphotography of AdWTStat5or AdDNStat5-treated CWR22Rv (72 h, MOI 8) and LnCap cells (96 h, MOI16).

FIG. 1E. Efficiency of adenoviral delivery of Stat5 proteins intoCWR22Rv and LnCap cells. Dose-dependent expression of WTStat5 or DNStat5in CWR22Rv and LnCap cells as detected by anti-panStat5 immunoblottingof whole cell lysates after 24 h of adenoviral exposure.

FIG. 2A. DNStat5-induced fragmentation of DNA in human prostate cancerlines CWR22Rv and LnCap, but not PC-3. DNA fragmentation analyzed bynucleosomal ELISA after exposure to AdDNStat5, AdWTStat5, AdLacZ,AdCtrl, or mock infection in CWR22Rv (48 h, MOI 8), LnCap cells (72 h,MOI 32), or PC-3 cells (72 h, MOI 32). A representative experiment ofsix independent repeats is shown; error bars represent SD of triplicatedeterminations.

FIG. 2B. DNStat5 induced apoptosis in CWR22Rv and LnCap cells asdetermined by flow cytometry. Cellular apoptosis detected as increasedhypodiploid fraction after treatment with AdDNStat5 or AdWTStat5,AdLacZ, AdCtrl, or mock infection in CWR22Rv (48 h, MOI 8), LnCap cells(72 h, MOI 32). The respective fractions of hypodiploid cells forCWR22Rv cells treated with AdLacZ, AdCtrl, or Mock, were less than 1.5%for both CWR22Rv and LnCap cells.

FIG. 2C. DNStat5-induced apoptosis is associated with Caspase-3activation. Caspase-3 activation was determined after exposure toAdDNStat5 and control conditions as indicated in CWR22Rv (36 h, MOI 8)and LnCap cells (48 h, MOI 32). A representative experiment of threeindependent repeats is shown; error bars represent SD of triplicatedeterminations.

FIG. 2D. DNStat5-induced Caspase-3 activation is associated withactivation of Caspase-9. CWR22Rv cells exposed to DNStat5 showedactivation of Caspase-9 at 36 h after initiation of treatment. Arepresentative experiment of three independent repeats is shown; errorbars represent SD of triplicate determinations.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are compositions and methods for inhibiting the growthof prostate cancer cells by inhibiting Stat5 activity. The methods andcompositions of the present invention can be used in relation to anytype of prostate cancer cell, including, for example, primary prostatecancer cells, advanced prostate cancer cells, and metastatic prostatecancer cells.

In certain embodiments, the subject invention relates to methods andcompositions for treating prostate cancer in a male. In certainembodiments, the invention relates to a method of treating prostatecancer in a male, comprising administering to the male an inhibitor ofthe activity of Stat5 in prostate cancer cells.

Identifying regulators of prostate cancer cell survival may lead to newtherapeutic strategies for prostate cancer. Applicants report prevalentactivation of transcription factor Stat5 in human prostate cancer andprovide novel evidence that blocking activation of Stat5 in humanprostate cancer cells leads to extensive cell death. Specifically, Stat5was activated in 65% of human prostate cancer specimens examined basedon nuclear location of tyrosine phosphorylated Stat5. Adenoviral genedelivery of a dominant-negative Stat5 mutant (DNStat5), but notwild-type Stat5, induced cell death of both the androgen-independenthuman prostate cancer cell line CWR22Rv and the androgen-sensitive LnCapcell line. Endogenous Stat5 was active in both CWR22Rv and LnCap cells.In contrast, only low levels of inactive Stat5 proteins were detected inthe PC-3 cell line, which correlated with resistance to DNStat5-inducedcell death. In CWR22Rv and LnCap cells, inhibition of Stat5 byexpression of DNStat5 induced apoptotic cell death, as judged frommorphological changes, DNA fragmentation, and Caspase-3 activation, withevidence of a Caspase-9 dependent mechanism. Applicants propose thatblocking Stat5 function may represent a novel therapeutic approach forprostate cancer.

Prostate cancer typically progresses to androgen-independent growthafter androgen-ablation therapy. Identification of androgen-independentproteins that control prostate cancer cell survival may lead to moreeffective therapies. Using long-term organ cultures of human and ratprostate tissues, Applicants have documented direct effects of prolactin(Prl) as a mitogen and survival factor for prostate epithelium (1-4).These observations have been complemented by demonstration of massivehyperplasia of prostates in transgenic mice over-expressing Prl (5,6),as well as reduced prostate sizes in Prl-null mice (7). Importantly,Applicants have also shown local production of Prl (1,8) and expressionof Prl-receptors in prostate epithelium (1,9) and, thereby, providedevidence for an autocrine loop of Prl action in prostate. Downstream ofPrl-receptor activation, Applicants have demonstrated that Stat5 is akey signaling protein in normal rat prostate epithelium (10), and thatdeficiency of Stat5 in Stat5a-null mice is associated with defectiveprostate tissue architecture (11).

Stat5 is one of 7 members of the Stat family of transcription factors inmammals (12), and consists of two distinct, but highly homologous,proteins, the 94-kDa Stat5a and 92-kDa Stat5b (13,14). In response toPrl, Stat5a and Stat5b become activated by phosphorylation on residueTyr694 and Tyr 699, respectively, in the C-terminal domain predominantlyby Janus tyrosine kinase-2 (Jak2), which is preassociated with thecytoplasmic domain of the Prl receptor (15). Tyrosine phosphorylatedStat5 proteins dimerize and translocate to the nucleus, where they bindto specific response elements of target gene promoters to regulatetranscription (16).

Based on previous findings of a survival function of Prl in normalprostate epithelium (4), an autocrine production of Prl by prostateepithelial cells (1,8), and the glandular defect of the prostates ofStat5a knock-out mice (11), Applicants hypothesized that Stat5 may actas a survival protein in human prostate cancer, and that blocking Stat5function could induce death of prostate cancer cells. Applicantsinvestigated activation of Stat5 in 40 human prostate cancer samples byimmunohistochemical analysis using activation-state specificanti-phosphoTyrStat5 antibody. To specifically block Stat5 activity inhuman prostate cancer cells, Applicants created a dominant-negativemutant of Stat5 (DNStat5) in an adenoviral transfer vector. As describedherein, Applicants demonstrate that transcription factor Stat5 isactivated in a significant number of human prostate cancer specimens andthat blocking Stat5 activity induces extensive apoptosis of prostatecancer cells.

The Signal Transducer and Activator of Transcription (STAT) family oftranscription factors provide a signaling link between cell surfacehormone and cytokine receptors and specific response elements in thepromoters of selective genes. Seven mammalian STAT genes have beenidentified. The Stat5 transcription factor is involved in regulation ofcell growth, differentiation, and cell survival based on data in breastepithelial cells and cells of the lymphohematopoietic system (Wakao,Gouilleux et al. 1994). Stat5 exists as two highly homologous isoforms,Stat5a and 5b, which have more than 95% amino acid homology and areencoded by separate genes (Liu, Robinson et al. 1995; Grimley, Dong etal. 1999). Stat5 is required for normal mammary epithelial celldevelopment and differentiation (Liu, Robinson et al. 1997; Udy, Towerset al. 1997; Moriggl, Topham et al. 1999).

Stat5 polypeptides typically are cytoplasmic and quiescent underhomeostatic conditions. Their activation results from phosphorylation ofthe highly conserved C-terminal tyrosine at Tyr694 in Stat5a or thecorresponding Tyr699 in Stat5b by certain intracellular tyrosinekinases. This phosphorylation permits dimer pair formation, which isneeded for Stat5 to bind to DNA.

This initial phosphotyrosyl “on-switch” is a generic Stat feature(Darnell 1997; Darnell 1998) and is triggered when cells with cognatereceptors are exposed to a variety of stimuli including cytokines,immune complexes, microbiologic agents or non-peptidyl compounds.Although the spectrum of agonists thus is heterogeneous, the bulkimplicated in triggering Stat5 activation belong to the class I andclass II cytokine superfamilies. (See Table 4 of (Grimley, Dong et al.1999). These cytokines utilize receptors lacking a catalytic domain(Liu, Gaffen et al. 1998), so that the Stat activation is most oftendependent upon an auxiliary protein kinase (Leonard and O'Shea 1998).

The Janus tyrosine kinases (Jaks) form biochemically stable associationswith class I and class II cytokine receptors. A non-covalent linkagefacilitates Jak phosphorylations during receptor ligation and increasesthe odds of interactions between Jaks and Stats recruited toreceptor-Jak complexes (Leonard and O'Shea 1998). This critical andconserved mutual relationship has engendered the scientific vernacularof “Jak-Stat pathway” (Liu, Gaffen et al. 1998). However, Jaks are notthe sole means of Stat activation.

Stat5a and Stat5b can also be tyrosine phosphorylated by a number ofcytokines commonly designated as “growth factors” which bind to receptortyrosine kinases (RTKs). The RTKs possess intrinsic catalyticproperties, and may trigger Stat5 signals absent a direct linkage to theJak enzyme system (Chen, Sadowski et al. 1997). In addition, Stat5tyrosine phosphorylation might be effected by cytosolic protein kinasesin the Src or Tec families. As “nonreceptor tyrosine kinases” (NTKs),the latter enzymes can function without extrinsic stimulation due toreceptor ligation. The Src-family kinase Lck has been implicated inStat5 phosphorylation during T cell proliferation (Welte, Leitenberg etal. 1999) and constitutively active NTKs, RTKs or analogous oncoproteinsmay be particularly significant in maintaining a constitutivephosphorylation of Stat5 in autonomously proliferating neoplastic cells(For example, See (Lacronique, Boureux et al. 1997; Wellbrock,Geissinger et al. 1998)).

In addition to the initial activation switch of Stat5, which involvesphosphorylation of a tyrosine residue within a conserved C-terminalsegment and causes dimerization of Stat5 molecules (Gouilleux, Wakao etal. 1994), a second coordinated activation event is required forfunctional activation. This involves translocation of dimerized Stat5from the cytoplasm into the cell nucleus, which permits Stat5 to come inproximity of and bind to gene regulatory promoter elements, and thusregulate transcription of specific genes (Gouilleux, Wakao et al. 1994;Kazansky, Kabotyanski et al. 1999). Because Stat5 not only requiresphosphorylation of a specific tyrosine residue, but also needs totranslocate into the cell nucleus in order to function as an activeDNA-binding transcription factor, amounts of tyrosine phosphorylatedStat5 located within the cell nucleus will reflect the levels ofactivated Stat5 more accurately than overall cellular levels of tyrosinephosphorylated Stat5. For instance, tyrosine phosphorylation of Stat5aby the Src tyrosine kinase has been shown not to be accompanied bynuclear translocation (Kazansky, Kabotyanski et al. 1999), illustratingthat quantitation of tyrosine phosphorylation status alone withoutassessing nuclear localization is not sufficient for accuratedetermination of levels of activated Stat5. Correspondingly, Stattranscription factors may become dephosphorylated within the cellnucleus and lose the ability to bind to DNA (Haspel and Darnell 1999),making assays that detect nuclear Stat5 protein levels alone also notsufficient for accurate determination of levels of activated Stat5. Inthe present application, the term “levels of activated Stat5” refers tolevels of tyrosine phosphorylated Stat5 within the cell nucleus.

Antibodies that bind exclusively to tyrosine phosphorylated Stat5 can beused to detect activated Stat5 in the nuclei of cells byimmunocytochemistry or immunohistochemistry, provided that proper stepsare taken to achieve antigen retrieval of this cryptic antigenic site.This antigenic site is cryptic, or unavailable, unless thephosphorylated tyrosine bound to the SH2 domain of the partner moleculein the dimer is dissociated by specific treatment.

Detection of active, tyrosine phosphorylated Stat5 byimmunohistochemistry in tissue sections has been reported (Jones, Welteet al. 1999; Ahonen, Harkonen et al. 2002; Nevalainen, Xie et al. 2002).The extent to which Stat5 promotes cell proliferation, cell survival, orinhibits growth by inducing cell differentiation in various tissues,including prostate gland, is unresolved. The possibility that inhibitingStat5 function would induce cell killing in human prostate cancer, orthat Stat5 activation status in prostate cancer is of predictive valuefor Stat5-suppressive prostate cancer treatment, was not obvious priorto the inventors' discovery, because a priori, it had been argued thatStat5 was not activated in human prostate cancer (Ni, Lou et al. 2002).Therefore, the present invention and description of a new therapy forprostate cancer based on inhibiting or blocking that activity of Stat5was unexpected based on the published literature and prevailing viewswithin the scientific field. As such, the role of Stat5 in humanprostate cancer development and progression had not been established,and its use as a marker of therapeutic response to the new therapy ofhuman prostate cancer had not been reported.

Applicants have invented a new strategy to induce apoptotic cell deathof prostate cancer cells by inhibition of transcription factor Stat5.This discovery can be used for development of a new therapy for prostatecancer.

The concept of transcription factor Stat5 as a survival factor andtherapeutic target in prostate cancer is completely novel andunexpected. Specifically, a study by Gao and colleagues (Ni, Lou et al.2002) indicated that in human prostate tissue homogenates there was onlya low level of Stat5 binding to an oligonucleotide probe correspondingto the Stat5 response element of the beta-casein promoter inelectrophoretic mobility shift assay (EMSA). However, using a highlysensitive in situ immunohistochemical detection technique (Nevalainen,Xie et al. 2002), which detects Stat5 activation at a single cell level,Applicants have now demonstrated that Stat5 is activated in humanprostate cancer with high frequency. This finding correspondstechnically to observations in human and mouse mammary gland whereactivation of Stat5 was difficult to detect outside pregnancy by EMSAassay using tissue homogenates, but was readily detectable byimmunohistochemical detection of activated Stat5 at single cell level(Nevalainen, Xie et al. 2002).

The novel finding of Stat5 activation in human prostate cancer, combinedwith previous studies (Nevalainen, Valve et al. 1996; Nevalainen, Valveet al. 1997; Nevalainen, Valve et al. 1997; Ahonen, Harkonen et al.1999; Nevalainen, Ahonen et al. 2000; Ahonen, Harkonen et al. 2002) ledApplicants to test whether inhibition of Stat5 would induce cell deathof human prostate cancer cells. However, in light of the publishedreport by Gao et al (Ni, Lou et al. 2002) it was completely unexpectedthat blocking Stat5 activity would induce cell killing.

Applicants have also discovered that detection of activated Stat5 inprostate cancer can predict responsiveness to the therapeutic strategyof the invention based on inhibition of transcription factor Stat5.

This is based on the correlation between endogenous Stat5 activation inprostate cancer cell lines and their sensitivity to inhibition of Stat5activity. Specifically, dominant-negative Stat5 gene therapy inducedcell killing in cells where endogenous Stat5 was active (e.g. CWR22,LNCaP) but not in cells where endogenous Stat5 was not active (e.g.PC-3). Therefore, a sensitive method that detects active Stat5 inprostate cancer cells, surgical biopsy or specimen, is expected topredict responsiveness to the new therapy. Predicting responsiveness isimportant so that patients can be selected who may benefit from thetherapy, while patients whose tumors are deemed unresponsive, may notneed to undergo this treatment.

In additional embodiments, the invention provides for the detection ofactivated Stat5 by methods including immunohistochemistry of activatedStat5, immunohistochemical detection of nuclear Stat5, and DNA-bindingassay of Stat5 for prediction of responsiveness of a male with prostatecancer for therapy based on inhibition of Stat5. “Inhibition of Stat5therapy” refers to therapy based on the inhibition of Stat5 activity.For example, in certain embodiments of the present invention, inhibitionof Stat5 therapy includes inhibiting the activity of Stat5a and/orStat5b polypeptides in a prostate cancer cell in a male in need oftreatment for prostate cancer. Inhibition of Stat5 therapy furtherincludes inhibiting the expression of Stat5 (e.g., Stat5a and/or Stat5b)polypeptides in a prostate cancer cell. Inhibition of Stat5 therapy canbe applied to any type of prostate cancer cell, including, for example,primary prostate cancer cells, advanced prostate cancer cells, andmetastatic prostate cancer cells.

In certain embodiments, the invention relates to agents that inhibitStat5 activity. Inhibitors of Stat5 include agents that inhibit theexpression of a Stat5 polypeptide. Inhibitors of Stat5 also includeagents that inhibit Stat5 activity. For example, such inhibitors includethose agents that inhibit activation of Stat5, such as agents thatinhibit Stat5 tyrosine phosphorylation and/or translocation ofphosphorylated Stat5 into the nucleus.

In certain embodiments, the present invention contemplates inhibitingStat5 in prostate cancer cells by inhibiting one or more of themolecules involved in Stat5 activation. For example, inhibitors of theinvention include agents that inhibit one or more of the moleculesinvolved in e.g., Stat5 phosphorylation (e.g., tyrosinephosphorylation), Stat5 translocation to the nucleus, and/or Stat5binding to DNA. Molecules involved in Stat5 activation includemolecules, such as tyrosine kinases (e.g., Jak2), that interact directlywith Stat5. Molecules involved in Stat5 activation also includemolecules, such as prolactin, that interact indirectly with Stat5.

Inhibitors of the invention include agents that inhibit phosphorylationof Stat5. For example, agents with phosphatase activity towardphosphorylated Stat5 are inhibitors of Stat5 that may be employed in themethods of the present invention. Examples of phosphatases includealkaline phosphatase, potato acid phosphatase, protein phosphatase 2A,and protein tyrosine phosphatase-1B (PTP-1B) (see suppliers such as,e.g., Amersham Biosciences, Sigma, and Calbiochem).

Inhibitors of the invention further include agents that inhibit Stat5tyrosine kinases, such as, for example, Jak2 inhibitors (e.g.,tyrphostin B42, supplied by e.g., Calbiochem) and Jak3 inhibitors (e.g.,PNU156804 described in Stepkowski, S M et al (2002) Blood99(2):680-689). Inhibitors of Jak1 and Tyk2 are also contemplated by thepresent invention.

Inhibitors of the invention additionally include agents that inhibitactivators of Stat5 such as inhibition of various growth factors andnon-receptor tyrosine kinases. For example, inhibitors of any of the Srcfamily tyrosine kinases are contemplated by the present invention asinhibitors of Stat5 activity in prostate cancer cells. Examples of Srcfamily kinases include Src, Fyn, Yes, Lck, Hck, Blk, Fgr, and Lyn. Anexample of an inhibitor of Src family tyrosine kinases includes PP2(supplied by e.g., Calbiochem).

Inhibitors of the invention further include agents that inhibit DNAbinding of Stat5. This may be achieved through the use of anelectrophilic inhibitor. Examples of electrophilic inhibitors includedisulfide benzamides and benzisothiazolone derivatives as described inWang, L H et al (2004) Nat Med 10:40-47.

In certain embodiments, the invention relates to agents that inhibitStat5 activity that are proteins that have dominant-negative Stat5function. Such proteins include, but are not limited to, mutated Stat5aor Stat5b, or genetic engineering of other related Stat genes, in wholeor in part, that would effectively result in dominant-negative functiontowards the activity of Stat5a and/or Stat5b. This would not be limitedto the Stat5aΔ713 mutant as described herein, but also othermodifications of Stat5a or Stat5b. Other variants of Stat5a or Stat5bhave been reported to act as dominant-negative Stat5 molecules(Yamashita, Iwase et al. 2003). Additionally, agents that inhibit Stat5activity include gene products that result in dominant-negative functiontowards the activity of Stat5a and/or Stat5b such as, for example,mutated Jak2 genes, which encode dominant-negative Jak2 polypeptides.Additionally, in certain embodiments, the invention relates to othervariants of Stat5 such as tyrosine phosphorylation deficient mutants ofStat5 or DNA binding deficient mutants of Stat5.

Therapeutic use of molecules that inhibit Stat5 activity include nucleicacids for delivery to prostate cancer cells, either by viral ornon-viral vectors. In certain embodiments, the invention relates toStat5 antisense therapy, using either oligonucleotide-based or geneexpression-based vectors; siRNA for Stat5, either oligonucleotide-basedor gene expression-based vectors; and small-molecule pharmacologicalinhibitors of Stat5 tyrosine kinase(s), such as, for example, inhibitorsof Jak2.

In certain embodiments of the invention, Stat5 activity is inhibitedthrough the use of antisense, ribozyme, RNAi, and other nucleicacid-related methods and compositions for inhibiting a Stat5 activity.Any of the nucleic acid therapies of the invention may be designed totarget a nucleic acid sequence represented in a Stat5 nucleic acid, suchas Stat5 nucleic acid disclosed in GenBank Accession Nos. NM_(—)003152and NM_(—)012448. In certain embodiments, any of the nucleic acidtherapies of the invention may be designed to target a nucleic acidsequence represented in a nucleic acid sequence of a molecule involvedin the activation of Stat5, such as, for example, Jak2 nucleic acidsequence disclosed in GenBank Accession No. NM_(—)004972.

The term “RNA interference” or “RNAi” refers to any method by whichexpression of a gene or gene product is decreased by introducing into atarget cell one or more double-stranded RNAs which are homologous to thegene of interest (particularly to the messenger RNA of the gene ofinterest). RNAi may also be achieved by introduction of a DNA:RNA hybridwherein the antisense strand (relative to the target) is RNA. Eitherstrand may include one or more modifications to the base orsugar-phosphate backbone. Any nucleic acid preparation designed toachieve an RNA interference effect is referred to herein as an siRNAconstruct. SiRNA includes short hairpin RNA (shRNA).

Certain embodiments of the invention make use of materials and methodsfor effecting knockdown of one or more Stat5 genes by means of RNAi.Additional embodiments of the invention make use of materials andmethods for effecting knockdown of one or more genes involved in theactivation of Stat5, such as, for example, Jak2. RNAi is a process ofsequence-specific post-transcriptional gene repression which can occurin eukaryotic cells. RNAi has been shown to be effective in reducing oreliminating the expression of genes in a number of different organismsincluding Caenorhabditiis elegans (see e.g., Fire et al. (1998) Nature391: 806-11), mouse eggs and embryos (Wianny et al. (2000) Nature CellBiol 2: 70-5, Svoboda et al. (2000) Development 127: 4147-56), andcultured RAT-1 fibroblasts (Bahramina et al. (1999) Mol Cell Biol 19:274-83), and appears to be an anciently evolved pathway available ineukaryotic plants and animals (Sharp (2001) Genes Dev. 15: 485-90). RNAihas proven to be an effective means of decreasing gene expression in avariety of cell types including HeLa cells, NIH/3T3 cells, COS cells,293 cells and BHK-21 cells.

The double stranded oligonucleotides used to effect RNAi are preferablyless than 30 base pairs in length and, more preferably, comprise about25, 24, 23, 22, 21, 20, 19, 18 or 17 base pairs of ribonucleic acid.Optionally the dsRNA oligonucleotides of the application may include 3′overhang ends. dsRNAs may be synthesized chemically or produced in vitroor in vivo using appropriate expression vectors. Synthetic RNAs include21 nucleotide RNAs chemically synthesized using methods known in the art(e.g., Expedite RNA phosphoramidites and thymidine phosphoramidite(Proligo, Germany). Synthetic oligonucleotides may be deprotected andgel-purified using methods known in the art (see e.g., Elbashir et al.(2001) Genes Dev. 15: 188-200). Longer RNAs may be transcribed frompromoters, such as T7 RNA polymerase promoters, known in the art. Asingle RNA target, placed in both possible orientations downstream of anin vitro promoter, will transcribe both strands of the target to createa dsRNA oligonucleotide of the desired target sequence. Any of the aboveRNA species may be designed to include a portion of nucleic acidsequence represented in a Stat5 nucleic acid, such as Stat5 nucleic aciddisclosed in GenBank Accession Nos. NM_(—)003152 and NM_(—)012448. RNAiconstructs of the invention further include RNAi constructs designed toinclude a portion of nucleic acid sequence represented in a geneinvolved in the activation of Stat5, such as, for example, Jak2. Methodsand compositions for designing appropriate oligonucleotides may befound, for example, in U.S. Pat. No. 6,251,588, the contents of whichare incorporated herein by reference. Further compositions, methods andapplications of RNAi technology are provided in U.S. Pat. Nos.6,278,039, 5,723,750 and 5,244,805, which are incorporated herein byreference.

In further embodiments, the invention relates to the use of isolated“antisense” nucleic acids to inhibit expression, e.g., by inhibitingtranscription and/or translation of a Stat5 nucleic acid. The antisensenucleic acids may bind to the potential drug target by conventional basepair complementarity, or, for example, in the case of binding to DNAduplexes, through specific interactions in the major groove of thedouble helix. In general, these methods refer to the range of techniquesgenerally employed in the art, and include any methods that rely onspecific binding to oligonucleotide sequences.

The antisense oligonucleotides can be DNA or RNA or chimeric mixtures orderivatives or modified versions thereof, single-stranded ordouble-stranded. The oligonucleotide can be modified at the base moiety,sugar moiety, or phosphate backbone, for example, to improve stabilityof the molecule, hybridization, etc. The oligonucleotide may includeother appended groups such as peptides or agents facilitating transportacross the cell membrane (see, e.g., Letsinger et al., 1989, Proc. Natl.Acad. Sci. U.S.A. 86:6553-6556, Lemaitre et al., 1987, Proc. Natl. Acad.Sci. 84:648-652, PCT Publication No. WO88/09810, published Dec. 15,1988) or the blood-brain barrier (see, e.g., PCT Publication No.WO89/10134, published Apr. 25, 1988), hybridization-triggered cleavageagents (see, e.g., Krol et al., 1988, BioTechniques 6:958-976) orintercalating agents. (see, e.g., Zon, 1988, Pharm. Res. 5:539-549). Tothis end, the oligonucleotide may be conjugated to another molecule,e.g., a peptide, hybridization triggered cross-linking agent, transportagent, hybridization-triggered cleavage agent, etc.

In certain embodiments, the invention relates to other nucleic acidtherapies to inhibit the activity of Stat5 in prostate cancer cells,including ribozymes, which are enzymatic RNA molecules capable ofcatalyzing the specific cleavage of RNA. (For a review, see Rossi (1994)Current Biology 4: 469-471) and DNA enzymes. Ribozyme molecules designedto catalytically cleave Stat5 mRNA transcripts can also be used toprevent translation of subject Stat5 mRNAs and/or expression of Stat5polypeptides. (See, e.g., PCT International Publication WO90/11364,published Oct. 4, 1990, Sarver et al. (1990) Science 247:1222-1225 andU.S. Pat. No. 5,093,246). DNA enzymes are designed so that theyrecognize a particular target nucleic acid sequence, much like anantisense oligonucleotide, however much like a ribozyme they arecatalytic and specifically cleave the target nucleic acid. Methods ofmaking and administering DNA enzymes can be found, for example, in U.S.Pat. No. 6,110,462.

RNAi, antisense, ribozyme, and DNA enzyme molecules of the applicationmay be prepared by any method known in the art for the synthesis of DNAand RNA molecules. These include techniques for chemically synthesizingoligodeoxyribonucleotides and oligoribonucleotides such as for examplesolid phase phosphoramidite chemical synthesis. Alternatively, RNAmolecules may be generated by in vitro and in vivo transcription of DNAsequences encoding the antisense RNA molecule. Such DNA sequences may beincorporated into a wide variety of vectors which incorporate suitableRNA polymerase promoters such as the T7 or SP6 polymerase promoters.Alternatively, antisense cDNA constructs that synthesize antisense RNAconstitutively or inducibly, depending on the promoter used, can beintroduced stably into cell lines. Moreover, various well-knownmodifications to nucleic acid molecules may be introduced as a means ofincreasing intracellular stability and half-life. Possible modificationsinclude but are not limited to the addition of flanking sequences ofribonucleotides or deoxyribonucleotides to the 5′ and/or 3′ ends of themolecule or the use of phosphorothioate or 2′ O-methyl rather thanphosphodiesterase linkages within the oligodeoxyribonucleotide backbone.

Agents contemplated by the invention also include compounds selectedfrom libraries of potential inhibitors of Stat5. There are a number ofdifferent libraries used for the identification of small moleculeinhibitors, including: chemical libraries, natural product libraries,and combinatorial libraries comprised of random peptides,oligonucleotides or organic molecules.

A wide variety of chemical libraries may be used. For example, chemicallibraries may be used that comprise random chemical structures, some ofwhich are analogs of known compounds or analogs of compounds that havebeen identified as “hits” or “leads” in other drug discovery screens,some of which are derived from natural products, and some of which arisefrom non-directed synthetic organic chemistry.

Natural product libraries include collections of products ofmicroorganisms, animals, plants, or marine organisms that are used tocreate mixtures for screening. Natural product libraries includepolyketides, non-ribosomal peptides, and variants (non-naturallyoccurring) thereof (reviewed in Science 282: 63-68 (1998)).Combinatorial libraries include those composed of large numbers ofpeptides, oligonucleotides, or organic compounds as a mixture.Combinatorial libraries include non-peptide combinatorial libraries.Still other combinatorial libraries include peptide, protein,peptidomimetic, multiparallel synthetic collection, recombinatorial,polypeptide, antibody, and RNAi libraries. For a review of combinatorialchemistry and libraries created therefrom, see Myers, Curr. Opin.Biotechnol. 8: 701-707 (1997). Identification of inhibitors through useof the various libraries described herein permits modification of thecandidate “hit” or “lead” to optimize the capacity of the “hit” tomodulate activity.

Antibodies can be used as modulators of the activity of a particularprotein, such as, for example Stat5 or receptors for prolactin.Antibodies can have extraordinary affinity and specificity forparticular epitopes. Antibodies can bind to a particular protein in sucha way that the binding of the antibody to the epitope on the protein caninterfere with the function of that protein. For example, an antibodymay inhibit the function of a Stat5 polypeptide by sterically hinderingthe proper interactions between the Stat5 polypeptide and anotherprotein or proper interactions with other molecules, or occupying activesites. Alternatively the binding of the antibody to an epitope on theparticular protein may alter the conformation of that protein such thatit is no longer able to properly function. Both monoclonal andpolyclonal antibodies (Ab) directed against a particular polypeptide,such as a Stat5 polypeptide or a prolactin receptor polypeptide, andantibody fragments such as Fab, F(ab)2, Fv and scFv can be used to blockthe action of a particular protein, such as Stat5.

Monoclonal or polyclonal antibodies can be made using standard protocols(see, e.g., Antibodies: A Laboratory Manual ed. by Harlow and Lane (ColdSpring Harbor Press: 1988). A mammal, such as a mouse, a hamster, a rat,a goat, or a rabbit can be immunized with an immunogenic form of thepeptide.

Variant polypeptides and peptide fragments can agonize or antagonize thefunction of a particular protein, such as the function of Stat5.Examples of such variants and fragments include constitutively active ordominant negative mutants of a particular protein, such as dominantnegative mutants of Stat5 or Jak2 as described herein. Antagonisticvariants may function in any of a number of ways, for example, asdescribed herein. One of skill in the art can readily make variantscomprising an amino acid sequence at least 60%, 70%, 75%, 80%, 85%, 90%,95%, 98% or 99% identical to a particular polypeptide, or a fragmentthereof, and identify variants that agonize or antagonize the functionof Stat5. Similarly, one can make peptide mimetics (e.g.,peptidomimetics) that agonize or antagonize the function of a Stat5polypeptide.

Toxicity and therapeutic efficacy of agents (drugs, compounds) of theinvention can be determined by standard pharmaceutical procedures incell cultures or experimental animals, e.g., for determining the LD₅₀(the dose lethal to 50% of the population) and the ED₅₀ (the dosetherapeutically effective in 50% of the population). The dose ratiobetween toxic and therapeutic effects is the therapeutic index and itcan be expressed as the ratio LD₅₀/ED₅₀. Compounds which exhibit largetherapeutic indices are preferred. While compounds that exhibit toxicside effects may be used, care should be taken to design a deliverysystem that targets such compounds to the site of affected tissue, suchas the prostate, in order to minimize potential damage to uninfectedcells and, thereby, reduce side effects.

The data obtained from the cell culture assays and animal studies can beused in formulating a range of dosage for use in humans. The dosage ofsuch compounds may lie within a range of circulating concentrations thatinclude the ED₅₀ with little or no toxicity. The dosage may vary withinthis range depending upon the dosage form employed and the route ofadministration utilized. For any compound used in the methods of theinvention, the therapeutically effective dose can be estimated initiallyfrom cell culture assays. A dose may be formulated in animal models toachieve a circulating plasma concentration range that includes the IC₅₀(i.e., the concentration of the test compound which achieves ahalf-maximal inhibition of symptoms) as determined in cell culture. Suchinformation can be used to more accurately determine useful doses inhumans. Levels in plasma may be measured, for example, by highperformance liquid chromatography.

Pharmaceutical compositions for use in accordance with the presentinvention may be formulated in a conventional manner using one or morephysiologically acceptable carriers or excipients. Thus, the compoundsand their physiologically acceptable salts and solvates may beformulated for administration by, for example, injection, inhalation orinsufflation (either through the mouth or the nose) or oral, buccal,parenteral or rectal administration.

For example, in certain embodiments, a composition of the inventioncomprises an RNAi mixed with a delivery system, such as a liposomesystem, and optionally including an acceptable excipient.

For such therapy, the compounds of the application can be formulated fora variety of loads of administration, including systemic and topical orlocalized administration. Techniques and formulations generally may befound in Remmington's Pharmaceutical Sciences, Meade Publishing Co.,Easton, Pa. Agents of the invention may be administered systemically,including injection intramuscularly, intravenously, intraperitoneally,and subcutaneously. Systemic administration can also be by transmucosalor transdermal means. Transmucosal administration may be through nasalsprays or using suppositories.

Agents of the invention may be formulated for parenteral administrationby injection, e.g., by bolus injection or continuous infusion.Formulations for injection may be presented in unit dosage form, e.g.,in ampoules or in multi-dose containers, with an added preservative. Thecompositions may take such forms as suspensions, solutions or emulsionsin oily or aqueous vehicles, and may contain formulatory agents such assuspending, stabilizing and/or dispersing agents. Alternatively, theactive ingredient may be in powder form for constitution with a suitablevehicle, e.g., sterile pyrogen-free water, before use.

Agents of the invention may also be formulated in rectal compositionssuch as suppositories or retention enemas, e.g., containing conventionalsuppository bases such as cocoa butter or other glycerides.

In addition to the formulations described previously, the compounds mayalso be formulated as a depot preparation. Such long acting formulationsmay be administered by implantation (for example subcutaneously orintramuscularly) or by intramuscular injection. Thus, for example, thecompounds may be formulated with suitable polymeric or hydrophobicmaterials (for example as an emulsion in an acceptable oil) or ionexchange resins, or as sparingly soluble derivatives, for example, as asparingly soluble salt.

For therapies involving the administration of nucleic acids, theoligomers of the application can be formulated for a variety of modes ofadministration, including systemic and topical or localizedadministration. For systemic administration, the agents may be injected,including intramuscularly, intravenously, intraperitoneally,intranodally, and subcutaneously for injection. The oligomers of theapplication can be formulated in liquid solutions, preferably inphysiologically compatible buffers such as Hank's solution or Ringer'ssolution. In addition, the oligomers may be formulated in solid form andredissolved or suspended immediately prior to use. Lyophilized forms arealso included.

The invention now being generally described, it will be more readilyunderstood by reference to the following examples, which are includedmerely for purposes of illustration of certain aspects and embodimentsof the present invention, and are not intended to limit the invention.

EXAMPLIFICATION Materials and Methods

Cell Culture. CWR22Rv, LnCap, and PC-3 cells (ATCC, Manassas, Va.) werecultured in RPMI-1640 medium (Biofluids, Gaithersburg, Md.) and T47Dcells (ATCC) in DMEM containing 10% fetal calf serum, 2 mM L-glutamine,and penicillin-streptomycin (50 IU/ml and 50 μg/ml, respectively) at 37°C. with 5% CO₂. LnCap cells were cultured in the presence of 1 nMdihydrotestosterone (5α-androstan-17β-ol-3-one; Sigma, Chemical Co.,MO).

Immunohistochemical Detection of Phosphorylated Stat5 in Human ProstateCancer.

Tissue sections of formalin-fixed prostate cancer samples from 40patients were immunostained for activated Stat5 as described previously(17). Briefly, tissue sections were de-paraffinized in xylene followedby re-hydration in graded alcohol. To unmask the epitopes, the slideswere microwave-treated with antigen retrieval solution AxAR1 (AdvantexBioReagents, Conroe, Tex.) or AxAR2 for use with anti-pTyrStat5 mAb oranti-panStat5 mAb, respectively. Endogenous peroxidase activity wasblocked by incubating the slides in 0.3% hydrogen peroxide, and thetissue sections were incubated in normal goat serum (BioGenexLaboratories Inc., San Ramon, Calif.) for 2 h to block unspecificbinding of immunoglobulins (IgGs). The anti-pTyrStat5 mAb was diluted in1% BSA in PBS at a final concentration of 0.6 μg/ml (AdvantexBioReagents). The anti-panStat5 mAb was used at a concentration of 2μg/ml (Advantex Bioreagents). Antigen-antibody complexes were detectedusing anti-mouse biotinylated goat secondary antibody followed bystreptavidin-horseradish-peroxidase complex (BioGenex).3,3′-diaminobenzidine was used as chromogen and hematoxylin ascounterstain. For negative controls, parallel slides were immunostainedwith subtype-specific mouse IgG, and lactating human mammary gland wasused as positive control tissue (17).

Generation of Adenovirus for Gene Delivery of Dominant-Negative andWild-Type Stat5.

Expression vector for murine Stat5a (pXM-Stat5a) was kindly provided byXiuwen Liu and Lothar Hennighausen (National Institutes of Health,Bethesda, Md.) (14). A dominant-negative (DN) variant of Stat5(Stat5aΔ713) was derived by truncation after amino acid residue Ala713of pXM-Stat5a, using a PCR fragment generated using5′-TAATACGACTCACTATAGGG-3′ (SEQ ID No. 1) (sense) and5′-GCTCTAGACTAGGCATCTGTGGATGCATTG-3′ (SEQ ID NO. 2) (antisense) primers,followed by EcoRI and XbaI digestion, and subcloning into theEcoRI-XbaI-digested pXM-Stat5a. The DNA sequence of the resultingconstruct pXM-Stat5aΔ713 was verified before use. The ability of ourDNStat5 (Stat5aΔ713) expression construct to completely suppress bothStat5a and Stat5b-mediated transcriptional activation has been reported(18). Replication-defective human adenovirus (Ad5) carrying wild-typeStat5 (WTStat5) or DNStat5 was generated using the AdEasy Vector system(Qbiogene, Carlsbad, Calif.). The open reading frame sequences ofDNStat5 and WTStat5 were released from respective plasmids by 1)digestion with EcoRI, 2) blunt-ending by Klenow DNA polymerase, and 3)digestion with HindIII, and the resulting fragments were subcloned intothe Klenow DNA polymerase blunt-ended BglII site and the unmodifiedHindIII site of the pShuttle-CMV transfer vector. Homologousrecombination of WTStat5 or DNStat5 transfer vectors with the pAdEasyvector was performed in BJ5183 E. coli by electroporation. Recombinedclones were screened by Kanamycin-resistant growth, and confirmed byPacI digestion to yield two bands of 30 kb and 4.5 kb. The recombinantviruses were packaged in QBI-293A cells and resulting clones wereselected from plaques and amplified. Expression of WTStat5 and DNStat5from adenoviral stocks was verified by Western blotting using ananti-panStat5 antibody (Transduction Laboratories, Lexington, Ky.).Selected recombinant viral stocks were expanded in large-scale cultures,purified by double cesium chloride gradient centrifugation, and titeredside-by-side by a standard plaque assay method in QBI-293A cells as perthe manufacturer's instructions.

Protein Solubilization and Immunoblotting.

Pellets of prostate cancer cells were solubilized in lysis buffer (10 mMTris-HCl, pH 7.6, 5 mM EDTA, 50 mM sodium chloride, 30 mM sodiumpyrophosphate, 50 mM sodium fluoride, 1 mM sodium orthovanadate, 1%Triton X-100, 1 mM phenylmethylsulfonylfluoride, 5 μg/ml aprotinin, 1μg/ml pepstatin A, and 2 μg/ml leupeptin). Cell lysates were rotatedend-over-end at 4° C. for 60 min, and insoluble material was pelleted at12,000×g for 30 min at 4° C. For immunoprecipitations, the proteinconcentrations of clarified cell lysates were determined by simplifiedBradford method (Bio-Rad Laboratories, Hercules, Calif.). The proteinswere analyzed by SDS-polyacrylamide gel electrophoresis andimmunoblotting using polyvinylidene difluoride membranes (Millipore,Bedford, Mass.). Blots were exposed overnight to primary antibodiesdiluted in blocking buffer at the following concentrations:anti-phosphotyrosine-Stat5a/b (Y694/Y699) mAb (Advantex BioReagents, TX,Conroe; 1 μg/ml), anti-panStat5 mAb (Transduction Laboratories, Inc.,Lexington, Ky.; 1 μg/ml) or polyclonal antisera to Stat5a (1:3,000) orStat5b (1:3,000). The blots were washed in washing buffer [50 mMTris-HCl (pH 7.6), 200 mM NaCl, 0.25% Tween 20], and incubated withhorseradish peroxidase-conjugated goat antibodies to mouse or rabbit IgG(Transduction Laboratories) (5 μg/ml). Enhanced chemiluminescencesubstrate (Amersham Pharmacia Biotech, Piscataway, N.J.) was usedaccording to the manufacturer's instructions for antibody detection.

Cell Viability Assay.

Cell viability was determined by a colorimetric assay in which atetrazolium compound is bioreduced by cells into a colored formazanproduct in direct proportion to the number of living cells in culture(Promega, Wis.). Prostate cancer cells were plated on 96-well plates (10000 cells/well) and infected the next day with different MOIs(multiplicity of infection) of adenovirus carrying either WTStat5,DNStat5 or LacZ. Cells infected with empty control virus ormock-infected cells served as additional controls. Three days after theinfection the assay was performed according to the manufacturer'sinstructions and the absorbance was recorded at 490 nm.

Cell Death Elisa Assay.

Fragmentation of DNA after cell death induced by inhibition oftranscription factor Stat5 was determined by photometricenzyme-immunoassay (Cell Death Detection ELISA ^(PLUS); Roche MolecularBiochemicals, Indianapolis, Ind.). Prostate cancer cells were plated on6-well plates and infected next morning with adenovirus carrying eitherDNStat5, WTStat5, LacZ, or with empty control virus. Cells were scrapedand centrifuged at 200×g, and cytoplasmic fractions containingfragmented DNA were transferred to streptavidin-coated microtiter platesthat had been incubated with biotinylated monoclonal anti-histoneantibody. The amount of fragmented DNA of nucleosomes bound toanti-histone antibody was evaluated by peroxidase conjugated monoclonalanti-DNA antibody using ABTS as a substrate at 405 nm.

Flow Cytometry.

CWR22Rv and LnCap cells (1×10⁶ cells/sample) were washed once in PBS,trypsinized, pelleted at 1,000×g, and washed once in 5 ml of cold PBS.After a second centrifugation, cells were resuspended in 0.5 ml of coldPBS and fixed by dropwise addition of 1.5 ml cold 100% ethanol, whileslowly vortexing the cell suspension. After having been fixed for 1 h at4° C., cells were stained with 100 μg/ml propidium iodide (RocheMolecular Biochemicals) and treated with RNase A (Invitrogen, Carlsbad,Calif.) for 30 min at 37° C. The cells were analyzed by flow cytometryusing a Coulter EPICS XL cell analyzer (Beckman-Coulter, Brea, Calif.).

Caspase-3 and Caspase-9 Activity Assays.

Activation of Caspase-3 (Roche Molecular Biochemicals) and Caspase-9(Oncogene Research Products, Boston, Mass.) were determined byfluorometric enzyme assays. Prostate cancer cells were plated on 6-wellplates and infected next morning with adenovirus carrying eitherDNStat5, WTStat5, LacZ or with empty control virus. Cells were scrapedand centrifuged at 500×g, and cytoplasmic fractions containing activatedCaspases were transferred to microtiter plates. Caspase-3 substrate(DEVD) or Caspase-9 substrate (LEHD) labeled with the fluorescentmolecule 7-amino-4-trifluoromethyl coumarin (AFC) were added to thesamples. Free fluorescent AFC was generated proportionally to the amountof activated Caspase in the cell lysate due to proteolytic cleavage ofthe substrate and determined fluorometrically at 505 nm.

Results and Discussion

Stat5 is Frequently Activated in Human Prostate Cancer.

Applicants have recently described a highly sensitive in situ detectionmethod for activation of Stat5 in paraffin embedded tissue which isbased on immunohistochemical detection of phosphorylated Stat5 that islocalized within the cell nucleus (10,17). This method, complementedwith immunohistochemical detection of nuclear Stat5 protein, was appliedto a material of 40 human prostate cancer specimens, and significantactivation of Stat5 was detected in 65% (26 of 40) of primary humanprostate cancer specimens of various Gleason scores. Representativesamples illustrating Stat5 activation by either phosphotyrosinedetection, or nuclear anti-Stat5 detection, within malignant humanprostate epithelia are presented (FIG. 1A, panels a and b,respectively). In contrast, Stat5 phosphotyrosine staining was negative(FIG. 1A, panel c) and nuclear immunostaining for Stat5 was absent inadjacent normal secretory prostate epithelial cells. Lactating humanbreast epithelium is presented as a positive control for tyrosinephosphorylated, activated human Stat5 (17), and parallel sections oflactating human breast stained with subtype-specific mouse IgG werenegative (FIG. 1A, panels d and e, respectively).

Stat5 is Activated in CWR22Rv and LnCap Cell Lines, but not in PC-3Cells.

Next, Applicants examined Stat5a and Stat5b protein expression andactivation in three human prostate cancer cell lines, including theandrogen-independent CWR22Rv and PC-3 cells, and the androgen-sensitiveLnCap cell line. For this analysis, immunoprecipitation of either Stat5aor Stat5b was followed by immunoblotting with the anti-phosphoTyrStat5antibody or with antibodies to either Stat5a or Stat5b. Stat5b was thepredominant Stat5 protein expressed in CWR22Rv and LnCap cells bothduring exponential growth (low density; LD) and in confluent cultureconditions (high density; HD; FIG. 1B). In both CWR22Rv and LnCap cellsat low and at high cell density, Stat5b was phosphorylated on thecritical Y699 residue. In contrast, no activation of Stat5a or Stat5bwas detected in PC-3 cells, consistent with low or undetectable levelsof Stat5 protein in these cells (FIG. 1B).

Blocking of Stat5 Activity in Human Prostate Cancer Lines Induces CellDeath.

Based on the prevalent activation of Stat5 in human prostate cancertissues, Applicants hypothesized that Stat5 may act as a survivalprotein in human prostate cancer. Therefore, Applicants tested whetherblocking Stat5 function in human prostate cancer cells would induce celldeath. To block activated endogenous Stat5 proteins in human prostatecancer, Applicants generated an adenovirus for effective delivery of adominant-negative mutant of Stat5 (DNStat5), and a matching controlvirus carrying wild type (WT) Stat5. The molecular construction of theadenoviral vector carrying dominant-negative Stat5a (AdDNStat5) and thematching control, AdWTStat5, is described in the Materials and Methodssection (See Example 2). Truncation of Stat5a after amino acid 713removes the entire transcriptional activation domain, and generates aStat5a mutant that is almost identical to the corresponding Stat5btruncated form. As expected, the Stat5a mutant effectively blocked thefunction of both WT Stat5a and Stat5b (18). Applicants have furthervalidated both the AdDNStat5 and the AdWTStat5 viral constructs infunctional assays, including assays for gene induction, inducibletyrosine phosphorylation, and DNA binding.

To determine whether blocking endogenous Stat5 activity would inducedeath of human prostate cancer cells, Applicants first examined theeffect of increasing doses of AdDNStat5 on the viability of theandrogen-independent CWR22Rv cell line. For the initial cell viabilitystudies Applicants used an assay determining the metabolic activity ofthe cells. CWR22Rv cells were cultured to 70% confluence in 96-wellplates, and exposed for 90 min to AdDNStat5 or AdWTStat5 at doses up toMOI 10, after which the virus was diluted 6-fold in culture medium asdescribed. After 96 h of infection, cells were analyzed for cellviability. A marked and dose-dependent effect of the expression ofDNStat5 on cell viability was observed, with detectable suppression atMOI 2.5, and suppression of cell viability by more than 90% at MOI 10(FIG. 1C). In contrast, cells infected with AdWTStat5 or AdLacZ did notshow significant loss of viability (FIG. 1C). Viability of CWR22Rv cellsinfected with an empty control virus (AdCtrl) was not reduced (notshown). The selective effect of AdDNStat5 in CWR22Rv cells wasconsistently observed in experiments that were repeated and reproducedmore than five times, and with four different, independently titeredbatches of virus.

Prostate Cancer Cell Death Induced by DNStat5 Represents Apoptosis.

Microscopic assessment of the effect of AdDNStat5 on CWR22Rv cellviability confirmed extensive cell death following expression ofDNStat5. CWR22Rv cells exposed to AdDNStat5 at MOI 8 for 72 h displayedextensive cell death as evidenced by cell rounding, detachment,shrinkage, and blebbing (FIG. 1D, panel b), which are morphologicalchanges consistent with apoptotic cell death. In contrast, there was noevidence of reduced cell viability in response to AdWTStat5 (FIG. 1D,panel a). Likewise, AdDNStat5, but not AdWTStat5, induced cell deathalso in the androgen-sensitive human prostate cancer cell line, LnCap(FIG. 1D, panels c and d). Dose response analyses showed that 2-4 foldhigher doses of virus were needed to induce cell death in LnCap cellscompared to CWR22Rv cells (not shown), an effect that correlated withless efficient adenoviral gene delivery of Stat5 proteins into LnCapcells. Specifically, dose-response analyses of viral protein deliveryrevealed that the same amount of virus induced lower levels of DNStat5or WTStat5 expression in LnCap cells than in CWR22Rv cells shown byimmunoblotting of whole cell lysates (FIG. 1E). FIG. 1E also indicatesthat cellular levels of DNStat5 and WTStat5 delivered by the respectiveadenoviral vectors are comparable, supporting the notion that theselective cell death observed in response to AdDNStat5 is due to itsspecific dominant-negative characteristics and not caused by othernonspecific mechanisms. In contrast, there were no signs of cell deathin PC-3 cells after 72 h exposure to AdDNStat5 at MOI 32 as judged fromcell morphology.

To further verify that DNStat5-induced killing of prostate cancer cellswas due to apoptotic cell death, prostate cancer cells were analyzed forDNStat5-induced fragmentation of DNA. CWR22Rv cells were exposed toAdDNStat5 and a set of controls at MOI 8 for 48 h. A selective effect ofDNStat5 on induction of DNA fragmentation was observed, as analyzed byan enzyme-linked immunosorbent assay (ELISA) of nucleosomal DNAfragments (FIG. 2A, panel a). On average, a seven-fold increase innucleosomal DNA fragmentation was detected in cells exposed to AdDNStat5over that detected in WTStat5 expressing cells (6 repeats, each with 3replicates/treatment group). Furthermore, DNStat5-induced death of LnCapcells was also associated with DNA fragmentation, as evidenced by aconsistent and more than six-fold increase in DNA fragmentation overlevels in AdWTStat5 treated cells on day 3 at MOI 32 (FIG. 2A, panel b)(6 repeats, each with 3 replicates/treatment group). Therefore,Applicants conclude that suppression of Stat5 induces apoptotic celldeath in both CWR22Rv and LnCap cells, as revealed by fragmentation ofDNA. In contrast, exposure of PC-3 cells, which do not express activeStat5, to AdDNStat5 did not increase fragmentation of DNA when comparedto cells expressing WTStat5 or to cells infected with empty controlvirus, AdLacZ, or mock-infected cells (FIG. 2A, panel c).

Apoptotic cell death of prostate cancer cells expressing DNStat5 wasalso verified by cell cycle analysis. In both CWR22Rv and LnCap cellsexpressing DNStat5, but not in cells expressing AdWTStat5, extensive DNAfragmentation was detected in the form of a large fraction ofhypodiploid cell fragments (FIG. 2B). In CWR22Rv cells, this proportionwas estimated to be approximately 8% of total cellular DNA at Day 3 ofAdDNStat5 infection using MOI of 8, which was 8-fold higher than thatobserved in parallel AdWTStat5-treated cells (0.9%). In LnCap cells, thefraction of cell fragments with hypodiploid DNA content increased 6-foldfrom 1.3% in AdWTStat5-treated cells to approximately 8% inDNStat5-treated cells. Mock-infected cells and cells infected with emptycontrol virus or AdLacZ were used as controls, and the fraction ofhypodiploid cells consistently remained below 1.3%.

DNStat5-Induced Apoptosis of CWR22Rv and LnCap Cells Involves Caspase-3Activation.

Proteolytic enzymes of the caspase family are critical mediators ofprogrammed cell death. A central role has been ascribed to Caspase-3 asa key executor of a major category of apoptotic cell death (19). Todetermine whether apoptosis in prostate cancer cells induced byexpression of DNStat5 is mediated by activation of Caspase-3, Applicantsanalyzed Caspase-3 activation by a specific Caspase-3 enzymatic assay.Exposure of CWR22Rv or LnCap cells to AdDNStat5 for 36 h or 48 h,respectively, activated Caspase-3 in both cell lines (FIG. 2C).Specifically, in CWR22Rv cells, activation of Caspase-3 was increased8-fold in cells expressing DNStat5 compared to AdWTStat5-infected cells.In LnCap cells the corresponding increase was approximately 2-fold (3repeats each with 3-replicates/treatment group). Therefore, Applicantsconclude that DNStat5-induced apoptosis in both CWR22Rv and LnCap humanprostate cancer cells involved activation of Caspase-3.

Caspase-3 mediated apoptosis may be induced through upstream activationof Caspase-9 in a Cytochrome C-dependent manner, or through Caspase-9independent mechanisms (20). Since suppression of Stat5 activation inCWR22Rv and LnCap cells induced activation of Caspase-3, Applicantswanted to determine whether DNStat5-induced activation of Caspase-3involved activation of Caspase-9. Caspase-9 activity was monitored inresponse to DNStat5 in both CWR22Rv and LnCap cells for up to 72 h. A6-fold induction of Caspase-9 was detected at 36 h in CWR22Rv cellsexpressing DNStat5 (FIG. 2D). In LnCap cells, the same trend wasobserved, but the effect was less striking. Applicants conclude thatDNStat5-induced cell death in CWR22Rv cells is mediated by Caspase-3through a Caspase-9 dependent mechanism. Caspase-9 activation furtherindicates a cytochrome C/Apaf-1 dependent apoptotic process (20).

The prevalent detection of activated Stat5 in primary human prostatecancer specimens indicates that Stat5 is a candidate therapeutic targetin a high proportion of prostate cancers. A recent study by Gao andcolleagues indicated that in human prostate tissue homogenates there wasonly a low level of Stat5 binding to an oligonucleotide probecorresponding to the Stat5 response element of the rat beta-caseinpromoter in electrophoretic mobility shift assays (21). It is possiblethat prostate cancer-specific or stromal factors interfere with bindingof Stat5 to this promoter when whole tissues are homogenized. In thisregard, using a highly sensitive in situ technique, which detects Stat5activation at a single cell level, Applicants have recently demonstratedthat Stat5 is activated in normal human and mouse mammary epithelialcells outside of pregnancy, an activity that is difficult to detect byEMSA using tissue homogenates of whole mammary glands (17).

The present work suggests that blocking activation of Stat5 in humanprostate is a potential new therapeutic approach. Delivery of suicidegenes into cancer cells is hampered by lack of effective deliverysystems, but gene therapeutic delivery systems are constantly improvingand involve both viral and non-viral strategies (22,23). Future prostatecancer gene therapy based on delivery of DNStat5 may therefore befeasible. On the other hand, small molecule inhibitors of the Stat5tyrosine kinase(s) responsible for Stat5 activation in prostate cancercould represent an alternative and more effective approach to inhibitStat5 in human prostate cancer with even more attractive pharmacologicalcharacteristics. Jak2 tyrosine kinase is a candidate target, since thisenzyme is responsible for tyrosine phosphorylation of Stat5 by a seriesof cytokine receptors, including receptors for prolactin (Prl).Prl-receptor associated signaling pathways are of particular interest,because Prl is produced locally in prostate epithelium indicating anautocrine loop of Prl action in prostate (1,8). In addition to Jak2,other tyrosine kinases, such as Jak1, Jak3 or Tyk2, as well as membersof the Src tyrosine kinase family, or receptor tyrosine kinases, arealso possible Stat5 kinases in prostate cancer (24).

Applicants show using in situ detection of phosphorylated and nuclearStat5 that Stat5 was activated in a majority of prostate cancerspecimens examined. This suggests that inhibition of Stat5 as atherapeutic approach could have a broad usefulness in the treatment ofprostate cancer. The observation that both androgen-refractory CWR22Rvand androgen-sensitive LnCap cells responded to suppression of Stat5with cell death, implies that apoptosis induced by blocking theactivation of Stat5 is independent of responsiveness to androgens.Furthermore, the correlation between endogenous Stat5 activation inprostate cancer cell lines and their sensitivity to DNStat5 indicatesthat immunohistochemical detection of activated Stat5 in prostate cancermay predict responsiveness to this therapeutic strategy.

REFERENCES

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INCORPORATION BY REFERENCE

All publications and patents mentioned herein are hereby incorporated byreference in their entirety as if each individual publication or patentwas specifically and individually indicated to be incorporated byreference. In case of conflict, the present application, including anydefinitions herein, will control.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. A method of inhibiting prostate cancer cell growth, comprisinginhibiting Stat5 activity in the prostate cancer cells, wherein Stat5activity is inhibited by contacting the prostate cancer cells with aninhibitor of Stat5 activity, wherein the inhibitor of Stat5 activity isan siRNA or an antisense RNA that is directed to a Stat5 nucleic acid,or a nucleic acid that encodes a mutated Stat5a or mutated Stat5b thathas dominant-negative Stat5 function.
 2. The method of claim 1, whereinthe inhibitor of Stat5 activity is an siRNA.
 3. The method of claim 2,wherein the siRNA inhibits the activity of a Stat5 polypeptide.
 4. Themethod of claim 3, wherein the Stat5 polypeptide is selected from thegroup consisting of: Stat5a and Stat5b.
 5. The method of claim 1,wherein the siRNA inhibits the expression of a Stat5 polypeptide.
 6. Themethod of claim 5, wherein the Stat5 polypeptide is selected from thegroup consisting of: Stat5a and Stat5b.
 7. The method of claim 2,wherein the siRNA comprises Stat5 nucleic acid.
 8. The method of claim7, wherein the Stat5 nucleic acid is selected from the group consistingof: Stat5a nucleic acid and Stat5b nucleic acid.
 9. The method of claim1, wherein the inhibition of Stat5 activity in the prostate cancer cellsresults in prostate cancer cell death.
 10. The method of claim 1,wherein the prostate cancer is primary prostate cancer, advancedprostate cancer, or metastatic prostate cancer.
 11. A method of treatingprostate cancer in a male, comprising administering to a male in need ofsuch treatment a therapeutically effective amount of an siRNA thatinhibits the activity of Stat5 polypeptide in prostate cancer cells ofthe male, wherein the siRNA inhibits the expression of a Stat5polypeptide.
 12. The method of claim 11, wherein the siRNA comprisesStat5 nucleic acid.
 13. The method of claim 12, wherein the Stat5nucleic acid is selected from the group consisting of: Stat5a nucleicacid and Stat5b nucleic acid.
 14. The method of claim 11, whereininhibition of the activity of Stat5 in prostate cancer cells of the maleresults in prostate cancer cell death.
 15. The method of claim 11,wherein the prostate cancer is primary prostate cancer, advancedprostate cancer, or metastatic prostate cancer.
 16. The method of claim11, wherein the Stat5 polypeptide is selected from the group consistingof: Stat5a and Stat5b.